Proteoglycans (PG) are recognized as important constituents of the mechanical properties of cartilage. However, the possibility that PG influence matrix quality by regulating cell functions has not been examined in detail and mechanisms of matrix assembly have not been examined. These processes are important for cartilage engineering and the proposal will establish the effect of PG on the assembly of neocartilage matrix and to use artificial polymers to direct this effort. The applicants have developed a rabbit articular chondrocyte culture model that allows biochemical, metabolic, morphological and biomechanical analyses. With this model it was demonstrated that polyethylene glycol as a surrogate for aggrecan to control osmotic pressure and exclude volumes increased PG synthesis and matrix content. The proposed studies will (1) test the hypothesis that the effect of exogenous aggrecan on matrix synthesis during the critical phase of matrix accumulation by cultured chondrocytes is due only to the osmotic properties of aggrecan; (2) determine how the structure of aggrecan or aggrecan substitutes promote assembly; (3) determine whether aggrecan promotes matrix assembly during the critical transitional phase by providing physical-chemical properties and not structural properties; (4) examine whether in the presence of adequate aggrecan the diameter of the collagen fibril will control the effectiveness of the collagen network in retaining aggrecan.